Olfactory marker protein regulation of glucagon secretion in hyperglycemia.

The olfactory marker protein (OMP), which is also expressed in nonolfactory tissues, plays a role in regulating the kinetics and termination of olfactory transduction. Thus, we hypothesized that OMP may play a similar role in modulating the secretion of hormones involved in Ca2+ and cAMP signaling, such as glucagon. In the present study, we confirmed nonolfactory α-cell-specific OMP expression in human and mouse pancreatic islets as well as in the murine α-cell line αTC1.9. Glucagon and OMP expression increased under hyperglycemic conditions. Omp knockdown in hyperglycemic αTC1.9 cells using small-interfering RNA (siRNA) reduced the responses to glucagon release and the related signaling pathways compared with the si-negative control. The OMPlox/lox;GCGcre/w mice expressed basal glucagon levels similar to those in the wild-type OMPlox/lox mice but showed resistance against streptozotocin-induced hyperglycemia. The ectopic olfactory signaling events in pancreatic α-cells suggest that olfactory receptor pathways could be therapeutic targets for reducing excessive glucagon levels.

Olfactory Receptor OR51E1 Mediates GLP-1 Secretion in Human and Rodent Enteroendocrine L Cells.

Glucagon-like peptide-1 (GLP-1) and peptide YY (PYY), produced by intestinal enteroendocrine L cells, are important gut hormones that coordinate gastrointestinal physiology, metabolism, and appetite. We aimed to investigate the role of olfactory receptor (OR) OR51E1 in GLP-1 and PYY secretion. We analyzed the expression of olfactory marker protein (OMP), an indicator of OR-mediated events in nonolfactory systems, in human intestinal L cells. Furthermore, we analyzed OMP and OR51E1 expression in the L cell line NCI-H716. To investigate whether odorant-activated OR signaling stimulates GLP-1 and PYY secretion, we used nonanoic acid, a known OR51E1 ligand. Treatment with 100 µM nonanoic acid increased GLP-1 secretion by 2.32 ± 0.41-fold and PYY secretion by 1.44 ± 0.10-fold; however, this effect was attenuated on small interfering RNA-mediated OR51E1 knockdown. Oral administration of nonanoic acid to rats resulted in a 2.89 ± 0.53-fold increase in GLP-1 levels and reductions in blood glucose levels compared with the control group. Nonanoic acid stimulates GLP-1 and PYY secretion via OR51E1 signaling in L cells, thereby indicating a potential role of OR-mediated events in GLP-1 and PYY secretion; this could be translated into a therapeutic approach in treating diabetes.

Olfactory marker protein regulates prolactin secretion and production by modulating Ca2+ and TRH signaling in lactotrophs.

Olfactory marker protein (OMP) is a marker of olfactory receptor-mediated chemoreception, even outside the olfactory system. Here, we report that OMP expression in the pituitary gland plays a role in basal and thyrotropin-releasing hormone (TRH)-induced prolactin (PRL) production and secretion. We found that OMP was expressed in human and rodent pituitary glands, especially in PRL-secreting lactotrophs. OMP knockdown in GH4 rat pituitary cells increased PRL production and secretion via extracellular signal-regulated kinase (ERK)1/2 signaling. Real-time PCR analysis and the Ca2+ influx assay revealed that OMP was critical for TRH-induced PRL secretion. OMP-knockout mice showed lower fertility than control mice, which was associated with increased basal PRL production via activation of ERK1/2 signaling and reduced TRH-induced PRL secretion. However, both in vitro and in vivo results indicated that OMP was only required for hormone production and secretion because ERK1/2 activation failed to stimulate cell proliferation. Additionally, patients with prolactinoma lacked OMP expression in tumor tissues with hyperactivated ERK1/2 signaling. These findings indicate that OMP plays a role in PRL production and secretion in lactotrophs through the modulation of Ca2+ and TRH signaling.

Biguanides Metformin and Phenformin Generate Therapeutic Effects via AMP-Activated Protein Kinase/Extracellular-Regulated Kinase Pathways in an In Vitro Model of Graves' Orbitopathy.

BACKGROUND: It was hypothesized that the biguanides metformin and phenformin, which are anti-hyperglycemic drugs used for diabetes mellitus, would have therapeutic effects in an in vitro model of Graves' orbitopathy (GO). Because adipogenesis, hyaluronan production, and inflammation are considered important in the pathogenesis of GO, this study aimed to determine the therapeutic effects and underlying mechanisms of biguanides on these parameters. METHODS: In vitro experiments were performed using primary cultured orbital fibroblasts from patients with GO. Orbital preadipocyte fibroblasts were allowed to differentiate into adipocytes and were treated with various concentrations of metformin or phenformin. Oil Red O staining was performed to evaluate lipid accumulation within the cells. Western blot analysis was used to measure the expression of adipogenic transcription factors and the phosphorylation of AMP-activated protein kinase and mitogen-activated protein kinase signaling proteins. Hyaluronan production was measured using enzyme-linked immunosorbent assay, and mRNA levels of proinflammatory molecules were determined using real-time polymerase chain reaction after interleukin (IL)-1ß stimulation with or without biguanide treatment. RESULTS: Lipid accumulation during adipogenesis in GO orbital fibroblasts was dose-dependently suppressed by both metformin and phenformin. Adipocyte differentiation was attenuated, and the adipogenic transcription factors peroxisome proliferator-activated receptor γ and CCAAT-enhancer-binding proteins-α/ß were downregulated. Furthermore, metformin and phenformin increased the phosphorylation of AMP-activated protein kinase and suppressed extracellular-regulated kinase activation. The IL-1ß-induced hyaluronan production and mRNA expression of IL-6, cyclooxygenase-2, and intercellular adhesion molecule-1 were also significantly suppressed after metformin or phenformin co-treatment. CONCLUSIONS: The present study indicates that the biguanides metformin and phenformin exert an anti-adipogenic and inhibitory effect on hyaluronan production and expression of pro-inflammatory molecules in GO orbital fibroblasts, suggesting that they could potentially be used for the treatment of GO.

4-Hydroxybenzaldehyde accelerates acute wound healing through activation of focal adhesion signalling in keratinocytes.

4-Hydroxybenzaldehyde (4-HBA) is a naturally occurring benzaldehyde and the major active constituent of Gastrodia elata. While recent studies have demonstrated metabolic effects of 4-HBA, little is known about the physiological role of 4-HBA in acute wound healing. Here, we investigated the effects and mechanisms of 4-HBA on acute wound healing. Using an in vitro approach, we found that 4-HBA significantly promoted keratinocyte cell migration and invasion by increasing focal adhesion kinase and Src activity. In addition, 4-HBA treatment also promoted wound healing and re-epithelialization in an in vivo excision wound animal model. Combination treatment with 4-HBA and platelet-derived growth factor subunit B homodimer showed synergistic effects in promoting wound healing. Taken together, our results demonstrated that treatment with 4-HBA promoted keratinocyte migration and wound healing in mouse skin through the Src/mitogen-activated protein kinase pathway. Therefore, 4-HBA could be a candidate therapeutic agent with the potential to promote acute wound healing.